1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor laser and, more particularly, a buried semiconductor laser.
2. Description of the Related Art
Compared with a liquid phase epitaxy method, a vapor phase epitaxy (VPE) method, especially an organometallic vapor phase epitaxy (OMVPE) method, has the following advantages:
(1) the VPE method can be applied to a large wafer,
(2) the VPE method has good controllability of the thickness of a layer, and
(3) the VPE method requires a short time in the growth process as a whole. Therefore, the VPE method has been employed to form a burying layer of a semiconductor laser. As a method of manufacturing a buried semiconductor laser (especially an InP long-wavelength laser) by an OMVPE method or the like, the following methods are proposed.
That is, as shown in FIG. 1A, a reverse triangular mesa 23 is formed using a stripe-like mask 22 formed on an InP cladding layer 21 as an etching mask, and, as shown in FIG. 1B, the reverse triangular mesa 23 is buried by a burying layer 24 using a VPE method. This method is disclosed in the Journal of Applied Physics vol. 64 (1988) pp.3884-3088.
In another related art, as shown in FIG. 2A, a rectangular mesa 31 is formed, and, as shown in FIG. 2B, the rectangular mesa 81 is buried by a VPE method. This method is disclosed in the Journal of Applied Physics vol. 64 (1988) pp.3684-3688, or the Journal of Crystal Growth vol. 93 (1988) pp.248-253.
In still another related art, a mesa is formed, and this mesa is buried by an VPE method, as shown in FIG. 3. This method is disclosed in the Journal of Applied Physics vol. 64 (1988) pp.3684-3688.
According to the first related art, as shown in FIG. 1B, nongrown portions (grooves) 25 are easily formed in the burying layer 24 near the bottom of the reverse triangular mesa 23 due to a lack of material diffusion from the vapor.
When the second related art is employed, a nongrown portions (grooves) is formed less than the first related art. However, in the second related art, a height 32 of the mesa 31 and an undercut amount 33 under a mask 34 must be limited in a predetermined range. According to the above literature, the mesa height is less than 3 .mu.m, and the undercut amount is about 1 .mu.m when the mesa height is 2.5 .mu.m.
According to the third related art for performing burying growth in a crystal orientation for forming a curved mesa, as shown in FIG. 3, a (111)A crystal plane is formed on a burying layer 41, and the burying layer 41 extends on the mask 42 along this crystal face. Therefore, the mesa cannot be buried in a flat surface.